Acrylonitrile-butadiene-stryrene (ABS) and corresponding blends of polycarbonate and acrylonitrile-butadiene-stryrene (PC/ABS) are routinely used as substrate parts in various electroplating applications, including for example in the manufacture of parts for the automotive sector. Typical automotive parts that undergo a chemical electroplating process include wheel-covers, door-handles, truck-grilles, tail lamp bezels and OEM logos. This decorative finishing serves a dual purpose of achieving aesthetic appeal along with added functionality of providing added protection against and resistance to environmental factors.
Acrylonitrile-butadiene-stryrene (ABS) polymers are derived from acrylonitrile, butadiene, and styrene monomers. ABS materials generally exhibit excellent impact resistance and toughness. In particular, ABS materials combine the strength and rigidity of the acrylonitrile and styrene polymers with the toughness of the polybutadiene rubber. Additionally, ABS exhibits excellent electroplate adhesion values. However, when compared to polycarbonate and ABS blends, neat acrylonitrile-butadiene-stryrene is typically used for applications with less stringent mechanical properties, such as tensile, flexural, heat, and fatigue requirements.
Polycarbonates (PC) are synthetic thermoplastic resins derived from bisphenols and phosgenes, or their derivatives. They are linear polyesters of carbonic acid and can be formed from dihydroxy compounds and carbonate diesters, or by ester interchange. Polymerization may be in aqueous, interfacial, or in nonaqueous solution. Polycarbonates are a useful class of polymers having many desired properties. They are highly regarded for optical clarity and enhanced impact strength, high heat resistance, and relative ductility at room temperature or below.
Blends of polycarbonates with ABS (PC/ABS) are amorphous thermoplastic blends that exhibit many desired properties combining the advantages and/or characteristics of both polycarbonate and ABS. For example, ABS can be incorporated into a polycarbonate blend as an impact modifier resulting in a PC/ABS blend having relatively high impact strength, heat resistance, good processability, weather and ozone resistance, good ductility, electrical resistance, aesthetic characteristics, etc. However, the polycarbonate component in PC/ABS blends typically leads to lower electroplate adhesion values of the resultant metal electroplated layers to the plastic substrate compared to neat ABS. Without wishing to be bound by theory, it is believed this is explained on the basis of butadiene and acrylonitrile from the ABS portion of the blend being the active species governing adhesion values. In contrast, the presence of excessive polycarbonate in a PC/ABS blend can lead to “bald-spots” of butadiene-deficient areas on molded surfaces where little or no metal-to-plastic adhesion is achieved, leading to possible failures such as worm-tracking, blistering, thermal-cycle, thermal-shock failures etc. Though various factors related to processing of the PC/ABS blends in secondary operations like injection-molding, as well as the electroplating process itself have a significant effect on the electroplate adhesion, the composition of the blend is considered to be one of the significant contributors to the final adhesion between the metal and plastic surface.
Accordingly, there remains a need in the art for thermoplastic blends of polycarbonate and acrylonitrile-butadiene-stryrene (ABS) exhibiting improved electroplate adhesion values notwithstanding the presence of polycarbonate in the blend. Additionally, there also remains a need in the art for methods that enable the manufacture of PC/ABS blends exhibiting relatively increased levels of polycarbonate without reducing or adversely impacting the desired level of electroplate adhesion. These and other advantages are provided by various aspects of the present disclosure.